1. Field of the Invention
The present invention relates, generally, to wireless data acquisition systems for data communications and, more particularly, to wireless data acquisition systems which employ small size, low power and low cost components and which may be adapted for different applications by software programming.
2. Description of the Related Art
All data acquisition systems generally operate in a similar fashion. They receive an external input from some type of sensing device, condition and/or convert the input to a format suitable for transmission, as necessary, and transmit it to another piece of equipment usually a monitor or controller, which may be a computer, and more specifically, a personal computer. The external input is generally an analog signal, although digital signals, frequently on-off switching, pulse-width modulation, or serial data protocols, are also involved. The inputs, though, come in many forms with many different characteristics, be they pneumatic, hydraulic or electronic, to list a few. Modern applications, control schemes and devices usually necessitate the use of electronic inputs in one form or another. For example, electronic analog inputs may have ranges of 4-20 mA, +/-5 volts, +/-15 volts, or microvolts to millivolts.
In the case of a wired system the analog input can be transmitted directly over interconnecting wiring with the major concern being that the interconnecting wires be suitably shielded to prevent interference by nearby electromagnetic sources. Signal conditioning becomes critically important for wireless systems, though. This is especially so when considering power consumption, size and cost factors. Because electronic inputs can have different characteristics (e.g.: high frequency or low frequency) and ranges (e.g.: microvolts to many volts), data acquisition systems are either application specific, i.e. designed to accept and condition a particular type of signal, i.e.: current, with a range of 4-20 mA for instance, or include separate discrete signal conditioning devices which consume a large amount of power and add considerable size.
Radio frequency (RF) wireless data acquisition systems can convert the input to a conditioned electronic signal which is used to modulate a carrier frequency which is then transmitted as a radio frequency signal to equipment in another location. The conditioned signal is encoded with data corresponding to the status of the input. The radio frequency signal is received, demodulated and decoded and the data is read, displayed, stored, and/or acted upon, i.e. monitored, analyzed, by equipment at the receiving point. In the United States the Federal Communications Commission (FCC) regulations govern RF transmissions, and similar agencies regulate RF transmissions in other countries, specifically as to the frequency band that can be utilized to transmit the signal and the strength of the signal. Other data transmission means, such as infrared, optical, or any means which does not require a mechanical connection is understood to offer similar advantages as RF transmission.
Wireless data acquisition systems are well known in the art. In the biomedical area, U.S. Pat. No. 5,704,351 to Mortara discloses a multiple channel biomedical digital telemetry transmitter. Mortara teaches an 8 channel biomedical transmitter specifically directed to electrocardiogram (EKG) signal transmission in the 902 to 928 MHz band. The Mortara device includes input circuitry and an analog-to-digital converter which receives the input signal from an EKG electrode and converts it to a digital signal which is inputted to a microprocessor. The microprocessor then converts the digital signal to a serial digital output signal which is used to frequency modulate the radio frequency carrier signal for telemetry transmission. The carrier frequency is adjustable within the 902 to 928 MHz band by two manual frequency setting switches. The use of these manual switches is the only adjustment available on the Mortara device and only to manually set the frequency within the 902 to 928 MHz band. The input circuitry and analog-to-digital converter are not adjustable nor adaptable to accept different input signal characteristics. In addition, the Mortara device cannot be adjusted, by programming or otherwise, to operate in any other frequency band. Finally, the Mortara device is just a transmitter and, therefore, is not able to receive RF or other signals to control its operation.
Similarly, U.S. Pat. No. 5,755,230 by Schmidt et al, discloses a device for monitoring a physiological signal, in this case EEG, and transmitting it by RF signal to a receiver. Like Mortara, the Schmidt device also cannot be modified or adjusted to receive inputs from different physiological sensors.
U.S. Pat. No. 5,579,775 to Dempsey, discloses a Dynamic Control of a Patient Monitoring System. Like Mortara and Schmidt, Dempsey '775 teaches a patient monitoring system with a telemetry subsystem which monitors and transmits an RF signal representing signals it receives from one or more physiological monitoring instruments. Unlike Mortara and Schmidt, Dempsey '775 teaches a receiving subsystem which can receive RF signals, in a backchannel arrangement to control the operation of the system. Dempsey '775, though, does not disclose or teach a system with the capabilities to adjust or modify input means, by software programming or otherwise, in response to different physiological signals. The device relies on separate monitoring sections in order to accommodate different physiological signals, i.e., EEG, ECG, SpO.sub.2 etc.
U.S. Pat. No. 5,417,222, also to Dempsey, discloses a portable processor interfaceable with a telemetry monitor at its I/O port. The Dempsey '222 device includes a telemetry monitor comprising a physiological monitor which receives selected physiological signals indicating a specific physiological condition of a patient. The physiological monitor is a specific type of monitor, i.e. one that reads signals of a specific physiological function, EKG for example. In the event that a different physiological function is to be monitored, i.e. EEG, a different physiological monitor must be employed. The device taught in this patent is designed to operate with basic physiological monitors already utilized in patient diagnostic services. Actually, the Dempsey '222 patent really only teaches the interface of a programmable processor, an example of which is given as Hewlett Packard 100LX palmtop processor (Hewlett Packard being listed as assignee of the patent) with a physiological monitor. Like the device in Dempsey '775, the device is not able to adapt or change the physiological monitor, by software or otherwise, to accept different physiological signals.
Fluke Corporation markets a wireless data acquisition system entitled "Wireless Logger".
The system is an integration of Fluke's Hydra Data Logger, a portable instrument monitor/analyzer, which accepts wired external inputs, with a RF modem. The Hydra Data Logger includes a universal input module which accepts and conditions the external inputs. The resulting signals are transmitted by the modem to another modem wired to a personal computer. The separate modem and universal input module are relatively large and consume up to 10 watts of power. In addition, the operation of the system is not software programmable. RF Neulink markets a similar system utilizing the VHF (136-280 MHz) and UHF (403-512 MHz) bands.
Accordingly, a need exists for a programmable wireless data acquisition system having a signal processing module which is capable of accepting multiple external inputs having different characteristics and ranges, and is able, through software programming, to convert and condition these external inputs, generate a radio frequency signal encoded with data corresponding to the external inputs, be frequency agile and adaptable, and transmit said radio frequency signal to a base station. In addition, a need exists for such a programmable wireless data acquisition system employing small size, low power consumptive and low cost components. Finally, a need exists for such a system which can accurately and dependably transmit data.